This invention pertains to an oil brake for vehicles such as all-terrain bikes, motor bikes, cars and the like.
From document U.S. Pat. No. 4,958,706 an oil brake is known in which, during compression, the piston expels the oil from a first working volume of the cylinder toward, on the one hand, a second working volume of the cylinder and, on the other, toward a backup chamber to the outside of which a gas is applied. During expansion, the oil moves from the second working volume and from the backup chamber toward the first working volume. The movable rod that holds the piston is tubular and contains a central rod that projects beyond the movable rod into the first working volume. At its end that is integral with the piston, the tubular rod has an inside diameter that is larger than the outside diameter of the central rod so as to form a central passage for the oil. A valve that is essentially shaped like a hat and is equipped with longitudinal slots is located in the opening of the tubular rod. The edge of the hat that is formed by the valve is superimposed on a heat-expanding stop valve and rests on the edge of the end of the tubular valve. The valve and the heat-expanding stop valve are kept resting on the end of the tubular rod in order to block the central passage by means of an open coil spring that is mounted on the central rod and rest on a washer that is integral with the latter. During expansion, the oil passes through an opening that is located in the cylindrical rod at the base of the piston into the second working volume, and then runs via the central passage around the hat-shaped valve and around the heat-expanding stop valve. The oil then moves into the first working volume through lateral openings that are located in the body of the piston and through an opening that is located in the end of a hat that is integral with the piston and surrounds the end of the central rod that projects into the first working volume. Control of the flow during expansion is accomplished by the two regulators that are the hat-shaped valve and the heat-expanding stop valve. Control of expansion at low oil speeds is accomplished by the heat-expanding stop valve, while control at high speeds is ensured by the openings on the hat-shaped valve. The pressure of the open coil spring can be adjusted by screwing down/unscrewing the central rod in the tubular rod, but the attachment end of the brake on the wheel axle must first be disassembled.
This kind of brake does not ensure adequate control of expansion, however. Thus, at high speed and at the end of its stroke, the piston may knock up against the bottom of the cylindrical body of the brake. Moreover, the system consisting of the stop valve and valve does not make it possible to control the start of expansion adequately since the flow of oil is released abruptly. In addition, the double mechanism for controlling the flows of oil during expansion at high and low speeds involves a significant number of complex parts which increase the cost of the brake; this is especially disadvantageous in the case of a brake for a bike, for example.